The correct answer is: D. Shared bus between the program memory and data memory
A von Neumann architecture is a computer architecture where the program and data share the same address space. This means that the program and data can be stored in the same memory locations, and the CPU can access both the program and data without having to switch between two different memory spaces.
A shared bus is a communication channel that allows multiple devices to share data. In a von Neumann architecture, the CPU, memory, and I/O devices all share a common bus. This allows the CPU to access memory and I/O devices without having to switch between different buses.
Options A, B, and C are incorrect because they do not describe the von Neumann architecture. Option A states that there is a separate bus between the program memory and data memory. This is not true in a von Neumann architecture, where the program and data share the same address space. Option B states that there is an external bus for program memory and data memory. This is also not true, as the CPU, memory, and I/O devices all share a common bus in a von Neumann architecture. Option C states that there is an external bus for data memory only. This is also not true, as the CPU needs to be able to access both the program and data memory, so there would need to be a way for the CPU to access both memory spaces.